1. Field of the Invention
The present invention relates to a variable nozzle mechanism of a turbocharger such as for an internal combustion engine.
2. Description of the Prior Art
For an internal combustion engine with a turbocharger, it is known that a variable nozzle mechanism, provided at the inlet of the turbine, effectively increases the output torque of the engine in a range of low engine speeds, because the boost pressure can be increased by throttling the inlet area of the turbine via the variable nozzle mechanism. Japanese Utility Model Publication SHO 58-82439, Japanese Utility Model Publication SHO 58-111324, Japanese Patent Publication SHO 58-176417 and Japanese Patent Publication SHO 50-94317 disclose such devices.
In the driving mechanism of nozzle vanes for the turbocharger disclosed in Japanese Utility Model Publication SHO 58-82439, the contents of which are incorporated herein by reference, guide means is provided at the outer surface of the center housing and a composite disk plate is rotatably supported by the guide means so as to have a common axis with the turbocharger. The rotation of the disk plate is transmitted via a ring plate coupled with the disk plate and a lever rotatably coupled with the ring to the nozzle vanes, thereby rotating the nozzle vanes. Since the flange portions for fixing the compressor housing and the turbine housing are integrally constructed with the center housing and have larger diameters than the inner diameter of the disk plate, the disk plate has to be manufactured in two portions, split along a diameter, in order to mount it onto the guide means and has to be assembled into a single composite annular plate by coupling the two separate portions after being mounted on the guide means. The separate portions are coupled together by the ring plate which is coupled with the disk plate at the outside periphery of the disk plate.
However, it was difficult to manufacture the composite disk plate so that its inner surface is a true circle as a result of the separate portions. Thus, the composite disk plate is likely to slide poorly with respect to the guide means and to momentarily bind during rotation. This decreases the reliability of the variable nozzle mechanism.